The overall performance of instrumentation or computer systems used for evaluating cardiac function is obviously limited by the quality of the signals on which diagnostic measurements are made. Signal quality can be maximized by interactive preprocessing during data acquisition. We propose to systematically study the problem of digital preprocessing of both the electrocardiogram and the echocardiogram. The electrocardiogram preprocessor will be designed to condition a short segment of three simultaneous leads for subsequent automatic off-line analysis by an established interpretation program. It will automatically control gain and calibration, limit artifact by rejecting records of poor technical quality, and correct procedural errors by alerting the technician to measurement inconsistencies. The echocardiogram preprocessor will transform ultrasonic echoes from a single transducer into a time-motion display in which each interface of interest is characterized by a single-valued function of time. The resultant display will be enhanced compared to that of conventional instrumentation and the signal will be in a format suitable for subsequent measurement. We plan to implement both preprocessors in a single microcomputer-based system. The trend in microcomputer development suggests that ultimately all processing can be economically carried out at the data acquisition site.